Antenna coupling apparatus for multiple receivers



Oct. 22, 1968 2. DWORKIN 3,407,366

I ANTENNA COUPLING APPARATUS FOR MULTIPLE RECEIVERS Filed Oct. 6, 1964 FIG.

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INVENTOR. H 26 004/410 Z fiwoele/lv H l 3; BY I FIG. 6 M

United States Patent Ofitice 3,407,366 ANTENNA COUPLING APPARATUS FOR MULTIPLE RECEIVERS Donald Z. Dworkin, Newark, N.J., assignor to Vikoa, Inc., a corporation of Delaware Filed Oct. 6, 1964, Ser. No. 401,907 9 Claims. c1. 333-9 ABSTRACT OF THE DISCLOSURE An antenna coupling apparatus for multiple receivers. The directional in which the coupler is used. The coupler is in a sense a rolled-up two-strip coupled device with two ground planes merged into a common cylinder.

The present invention relates to apparatus for provid ing multiple receivers such as television receivers with input signals for adjusting such apparatus.

It has become a widespread practice and the coaxial line from the master antenna floors. In achieving these objects, an illustrative form of by each directional coupler via a novel ture connected to the branch line of the pier.

A further object of the invention resides in the provision of multi-tap strucdirectional cou- Vision of a multi-tap line of remarkable simplicity, eco- 3,407,366 Patented Oct. 22, 1968 nomical to manufacture, and of excellent operating characteristics The nature of the invention, including the foregoing and other objects and novel features, will be more fully appreciated by referring to the following detailed descrip- FIGURE 2 is a transverse cross-section of the device in FIG. 1, as viewed from the line 22 in FIG. 1;

FIGURE 3 is a longitudinal cross-section of a component forming part of the distribution unit in FIG. 1; FIGURE 4 is a right-hand end view of the component in FIG. 3;

FIGURE 5 is a greatly enlarged cross-sectional detail in a portion of d In FIGS. 1 and 2, a metal housing 10 is shown, conveniently formed as a casting, open at the bot-tom and closed at the top 12. A first coaxial coupling 14 is mounted at the left side of housing 10 and another coaxial coupling 16 is mounted at the right side of the and 16 in an antenna system. connectors 14 and 16 are conhelical main-line conductor 18 The helical branch-line conductor 26 of directional coupler 20 has its right-hand end (as viewed in FIG. 1) connected by a terminating resistor 28 to the shield and, thus, to ground. The left-hand end of branch line 26 is 30a of a resilient metal strip 30 of uniform width, forming part of a multi-tap groundspacer tubes 36 of insulation. The spacing between conductors 30 and 32 is uniform, and is established by the length of tubes 36. Resilient-tongued washers 38 are pressed onto the ends of rods 34 to retain parts 30, 32, 34 and 36 in assembly as illustrated.

The width of strip conductor 30 is calculated in relation to the spacing of strip conductor 30 from groundplane plate 32; and (subject to empirical correction) these are related in a manner to yield the desired characteristic impedance. This characteristic impedance is modified to a minimal extent by the proximity of conductor 30 to grounded shield 22 and to the inside of housing 10, and this may be taken into account in adjusting the dimensions of the strip transmission line 30, 32. A resistor 40 has one terminal connected to plate 32 and thus grounded, and the opposite terminal of resistor 40 is connected to the end 30b of line 30 which is remote from the input end 30a of strip 30 of the ground-plane or strip transmission line.

Between the input end 30a and output end 30b of line 30 there are a number of resilient tongues 30c, one of which is shown in cross-section in FIG. 1. These tongues are disposed approximately in the plane of conductor 30, and depart from that plane only to a minimal extent necessary to constitute resilient taps. Plate 32 has a number of internally threaded extrusions 32a which receive standard resistive coaxial connectors 42. As many connectors 42 may be used as .there are extrusions 32a and tongues 300, for a corresponding number of separate receivers that may be accommodated by the distribution unit in FIGS. 1 and 2. Each resistive connector includes an outer conductor and an endwise projecting inner conductor 42a. When resistive connectors 42 are screwed tightly into the extruded formations 32a, the shoulders of connectors 42 butt against plate 32 and at that time the projecting center conductor 42a has been forced into firm pressure engagement with a tongue 30c. The tongue is deflected somewhat as a result of the positive advance of connector 42.

The system in which the unit of FIGS. 1 and 2 is to be used includes an antenna A (FIG. 6) which may be connected directly ,to main line 18 of the directional coupler 20 or a number of additional directional couplers 20 may be interposed between antenna A and the directional coupler 20 shown in FIG. 6. The opposite end of the main line 18 extends to the termination as shown, and a number of additional directional couplers 20 may correspondingly be interposed between ground and the particular directional coupler shown in FIG. 6. As previously described, resistor 28 is interposed between one end of branch line 26 and ground, and the other end of branch line 26 is connected to metal strip or conductor 30 of the ground-plane transmission line. The opposite end of conductor 30 is connected through resistor 40 to ground-plane plate 32. A reasonable number of resistive taps or connectors 42 may be mounted in plate 32, engaging strip conductor 30 as previously described, for providing signal input to a corresponding number of television receivers or the like.

Directional coupler 20 is shown in greater detail in FIGS. 3, 4 and 5. As seen in these figures, the directional coupler 20 includes a coil form 44, this being a thin-wall low-loss cylinder of insulation. Lines 18 and 26 are wound on form 44 as accurately spaced pairs of conductors. Advantageously, these conductors are thin narrow ribbons that are embedded in a thin strip of high-quality low-loss insulation so as to form a twin conductor unit 46 as shown in FIG. 5. By proper choice of proportions, the spacing between conductors 18 and 26 of one strip 46 can be made the same as the spacing between conductor 26 of one turn of strip 46 and conductor 18 of the next adjoining convolution of strip 46 around form 44. In alternative forms of construction, the conductors 18 and 26 may be formed directly on insulating tube 44, as by means of well known printed-circuit or photo-etch techniques.

Metal shield 22 encloses the form 44 and its conductors 18 and 26, and is spaced radially away from helical conductors 18 and 26, uniformly, from one end of coil form 44 to the other. In the form of construction shown, this spacing is established by means of a layer 48 of resilient low-loss insulating foam, such as polyurethane for example. This foam advantageously extends all the way around the double helical conductors 18 and 26.

As seen in FIG. 4, shield 22 has a narrow bead or rib 22b extending all along its length, and shield 22 is made of relatively thin-walled metal, ductile and readily bendable in achieving a further feature of the invention. It will be appreciated that conductors 18 and 26 are both spaced equally and uniformly from grounded shield 22, and consequently each conductor 18 and 22, considered separately, forms a strip transmission line in relation to shield 22. By carefully adjusting the spacing between shield 22 and both of these conductors 18, 26, the characteristic impedance of both helical conductors of directional coupler 20 can be matched to the characteristic impedance of the coaxial conductor system between antenna A and ground. Line 30, 32 also has the same characteristic impedance.

The adjustment of shield 22 for establishing the proper characteristic impedance of the directional coupler can be achieved by means of an appropriately shaped pair of jaws which conform closely to the cylindrical contour of shield 22 in its limited range of adjustment, or alternatively, a tool can be provided for adjustably squeezing the walls of rib 22b together and thereby pulling the shield more tightly around the coils 18, 26 and coil form 44 Within the shield. This squeezing operation is carried out while V.S.W.R. measuring instruments are being observed, and the progressive narrowing of rib 22b is interrupted when the desired characteristic impedance is reached. A ratio of 1 to 1.15 is readily achieved, consistent with the desired attenuation of the signal coupled into the branch circuit 26, and consistent with adequate discrimination against signals from the circuit apparatus connected to strip 30.

The fact that conductors 18 and 26 are helical makes it possible to construct a directional coupler of relatively compact proportions despite the requirement that conductor 26 should be nominally one-quarter of a wavelength long at the mid-brand frequency for which the coupler is to be used. The cylindrical conductor 22 is uniformly spaced from conductors 1'8 and 26 and establishes the characteristic impedance of both the main line and the branch line, these being the same in the construction shown. Being adjustable in diameter, conductor 22 can be adjusted to establish the desired characteristic impedance of line 18-22 as well as of line 26-22, thereby to match the characteristic impedance of the connectors 14, 16 and of tap-off line 30, 32. Being disposed outside the helical conductors 18 and 26, conductor 22 acts as a shield in addition to its transmission line function of ground-plane conductor.

From the foregoing it is evident that there has been provided a directional coupler of compact dimensions for signals whose wave-length would ordinarily call for a considerably longer structure; a directional coupler having excellent forward-wave versus return-wave discrimination; a directional coupler whose characterisic impedance can be readily adjusted. Further there has been provided a novel multi-tap strip or ground-plane line for connection to connectors, usually resistive connectors of respective receivers; a structure that readily and with elemental forms provides for connection of multiple coaxial connectors; and a multi-tap line whose dimensions are not critical yet whose characteristic impedance is readily made to equal that of the connected apparatus. Still further, there has been provided a unitary assembly having an exemplary directional coupler and multi-tap line connected together as a distribution unit for coupling out of a master antenna system a desired sample of the antenna signal while minimizing the tendency of reversecoupling of signals and for connecting the output of the directional coupler to a group of resistive couplers that supply signals to a corresponding number of receivers. It will be recognized that the foregoing represents a presently preferred embodiment of the invention in its various aspects; but it may be variously modified and utilized by those skilled in the art and certain novel features may be adopted without using others; and consequently the invention should be interpreted broadly in accordance with its full spirit and scope.

What is claimed is:

1. In a distribution system for television receivers and the like having a coaxial conductor system having a characteristic impedance, a directional coupler including a cylindrical coil form of insulation, paired main-line and branch-line helical conductors having successive turns about said coil form with the turns of the main-line helical conductor alternating along the coil form with the turns of the branch-line conductor, and a substantially cylindrical metal shield encasing both said conductors and spaced substantially uniformly and equally therefrom such that the characteristic impedance of both of said helical conductors matches said system characteristic impedance.

2. A distribution system for television receivers and the like in accordance with claim 1 further including a terminating resistor connected between one end of said branchline conductor and said sheld.

3. A directional coupler for a coaxial conductor system having a characteristic impedance, including a cylindrical metal shield and first and second paired helical conductors within said shield and spaced substantially uniformly and equally therefrom, said helical conductors being spaced substantially uniformly from each other and having successive helical turns occurring in alternation along the shield, said shield being spaced from said helical conductors such that the characteristic impedance of both of said helical conductors matches said system characteristic impedance.

4. A directional coupler, including a cylindrical metal shield and first and second paired helical conductors within said shield and spaced substantially uniformly and equally therefrom, said helical conductors being spaced substantially uniformly from each other and having successive helical turns occurring in alternation along the shield, and insulating means interposed between said shield and both said helical conductors, said insulating means including a spongy, squeezable layer and being effective to center the shield coaxially about said helical conductors and thereby to provide uniform spacing between said shield and said conductors.

5. A directional coupler, including a cylindrical metal shield and first and second paired helical conductors within said shield and spaced substantially uniformly therefrom, said helical conductors being spaced substantially uniformly from each other and having successive helical turns occurring in alternation along the shield, a pair of coaxial connectors each having an inner conductor and an outer conductor, the inner conductors of said connectors being connected to respective ends of said first helical conductor, the outer conductors of said connectors being connected to said shield, and a terminating resistor connected between one end of said second helical conductor and said shield.

6. A directional coupler for a coaxial conductor system having a characteristic impedance, including a main helical conductor, a substantially cylindrical conductor coaxial with and spaced substantially uniformly from said main helical conductor, the latter having successive turns spaced apart along the cylindrical conductor, a branch helical conductor having successive turns interposed between the turns of said main helical conductor, and insulation interposed between said cylindrical conductor and both said helical conductors, said substantially cylindrical conductor being equally spaced from said 6 main and branch helical conductors such that said main and branch helical conductors have characteristic impedances matching said system characteristic impedance.

7. A distribution unit for an antenna system to supply signals to multiple television receivers and the like, including a metal housing, a directional coupler within said housing and including a substantially cylindrical metal shield connected to the housing, and main and branch helical conductors coaxially within said shield and having successive turns occurring alternately along said cylindrical shield and spaced uniformly therefrom, a pair of coaxial connectors extending through said housing and having inner conductors connected to respective ends of said main helical conductor, a tap-off line within said housing and including a ground-plane conductor connected to said housing and having threaded apertures for receiving coaxial tap-01f devices, said tap-off line further including an elongated strip of resilient metal spaced substantially uniformly from said ground-plane conductor and having tongues opposite said threaded apertures, said elongated strip and said ground-plane conductor being proportioned to have the same characteristic impedance as that of a line comprising said branch helical conductor and said cylindrical shield, one end of said branch helical conductor having a connection to one end of said strip, the opposite ends of said branch helical conductor and said strip having respective terminating resistors electrically connected to said housing and each having a resistance that equals said characteristic impedance.

8. In a distribution system for television receivers and the like, a tap-off line and a series of coaxial tap-off devices connected to said line, each of said tap-off devices having an outer conductor and anendwise projecting inner conductor, said tap-off line including a groundplane conductor having a series of apertures for receiving respective tap-off devices, a strip of resilient metal extending along said apertures, said strip having integral tongues opposite said apertures and engaged by said endwise-projecting inner conductors, insulating supports separating said strip uniformly from said ground-plane conductor, said strip being of substantially uniform width, the dimensions and spacing of said strip in relation to said ground-plane conductor providing a characteristic impedance that substantially matches that of said tap-off devices.

9. An adjustable directional coupler including a coil form, main and branch helical conductors on said coil form having uniformly spaced-apart helical turns occurring in alternation along the coil form, a ductile metal shield about the helical conductors, and insulating means providing substantially uniform separation of said shield from said helical conductors, said insulating means including a spongy layer, and said shield incorporating a deformable shield-diameter adjusting formation.

References Cited UNITED STATES PATENTS 2,054,799 9/1936 Kautter 343-852 X 2,145,548 1/1939 Landon 336-84 X 2,531,438 11/1950 Jones 343-858 X 2,925,565 2/1960 Cook et al. 333-l0 X 3,209,284 9/1965 Hast 333-10 3,267,394 8/1966 Peil et al 333-84 X 3,280,364 10/1966 Sugawara et al. 333-10 X ELI LIEBERMAN, Primary Examiner. PAUL GENSLER, Assistant Examiner. 

